About make an audio power amplifier.

[Nikolai Petrenko]

I

Hi Nikolai,

Nice decoupling, but not sure what the 6 x 15V Zeners will do (have I misunderstood your schematic). Go for voltage regulators, which would be much much better. You can get 100mA regulators which are small and cheap- sorry.

spec

I mean 6 pieces of 15V zenner diodes.
I have thought about use TO-92 regulators instead of TO-220 before but sorry to say: small regulators like 78L05; 78L08; 78L09 and 78L12 are available but 78L15 and higher voltages aren't, LM317L too.

 

[Nikolai Petrenko]

3 zenner diodes in parallel can provide current up to 60mA to feed preamps without any damage, because my zenner diodes can't allow current over 30mA or they will burn.

 

[spec]

I

I mean 6 pieces of 15V zenner diodes.
I have thought about use TO-92 regulators instead of TO-220 before but sorry to say: small regulators like 78L05; 78L08; 78L09 and 78L12 are available but 78L15 and higher voltages aren't, LM317L too.

Nikolai,

No worries: it is a simple matter to configure most regulators for a higher voltage. So for example you could turn a 78L05 into a 15V regulator with a couple of resistors, if I remember correctly

spec

 

[spec]

3 zenner diodes in parallel can provide current up to 60mA to feed preamps without any damage, because my zenner diodes can't allow current over 30mA or they will burn.

Not really practical Nikolai, because 6 of 15V Zeners would all have different voltages and slope resistance so you would not achieve much by paralleling them up.

One approach would be to make your own voltage regulator with a 15V Zenner and a couple of transistors. For low current outputs, you can even make a regulator from just an opamp and a Zener. But as said in my previous post, a standard voltage regulator is the way to go. If you let me know what regulators you can get, I will post a schematic for a good 15V regulator.

spec

 

[cowboybob]

Given your stated load requirements, you gain nothing by using 3 zeners in parallel AND the rail voltage will reflect the Lowest of the three's BV. One zener (per rail) is preferred (as noted by spec above).

Sample SIM:

All things considered, this circuit is at the edge of various limits.

The 270Ω current limiters may need to be adjusted depending on the load. Choose a value that allows the zener to regulate AND still allows the circuit to provide adequate current for your OPAs. Rail voltages will also vary with load resistance(s).

Once you have one rail working correctly, mirror it for the other rail.

 

[spec]

Re using a lower voltage reg to generate 15V, here is the sort of circuit to do the job. There are many variations of this:

ERRATA
(1) The maximum input voltage should read 45V, not 50V (thanks Mikebits)

 

[large_ghostman]

Re using a lower voltage reg to generate 15V, here is the sort of circuit you could use. There are many variations of this:

**broken link removed**
​

ERRATA
(1) Zener should be 10V, not 5V6
(2) Output voltage should be 15V, not 15V6

I like that!

Zeners seem to be prone to heat fluctuations as well, seeing as your building a super duper amp it seems a shame to ruin it by using cheap shortcuts.

 

[spec]

I like that!

Hi LG,

The main problem with the shunt Zenner circuit is that it does not isolate noise and ripple that well (rejection ratio). Also the circuit does not generate a super low impedance power line, which is important for minimizing distortion, especially with a discrete pre amp, which Nikolai favors.

spec

 

[Mikebits]

You might want to take a look at the maximum input voltage spec of that regulator. I think it is 30 or 35v.

 

[Nigel Goodwin]

3 zenner diodes in parallel can provide current up to 60mA to feed preamps without any damage, because my zenner diodes can't allow current over 30mA or they will burn.

Historically such schemes (but ONLY using single zeners - you can't parallel them) were commonplace in guitar and PA amplifiers, feeding the preamp stages from the main amplifier rails.

However, as you would expect, this part of the circuit was always a serious source of problems and failures, due to the high amount of heat dissipated there.

Simply use a pair of 7815/7915, or the smaller L series - it will perform FAR better, and be much more reliable.

 

[Mikebits]

Simply use a pair of 7815/7915, or the smaller L series - it will perform FAR better, and be much more reliable.

He said he can't get those, for what ever reason?

 

[spec]

You might want to take a look at the maximum input voltage spec of that regulator. I think it is 30 or 35v.

Thanks Mike.

The input output differential is as you say, 35V but as the output voltage is 15V this means that the total maximum safe input voltage to that circuit implementation is 35V + 15V =50V.

CORRECTION: you are right the tail of the 78L05 is at 10V so that reduces the safe input safe voltage to 35V +10V = 45V. Good work

Of course, it would be sensible to pop in a few protection bits here and there to legislate for turn on conditions and possible fault conditions. If the reverse diode were a 33V Zener, for example, that may help.

Keep the comments cumming. Like I have said before, my schematics are straight off the drawing board and may be full of errors. It is a great help to know that someone is checking.

Cheers

spec

 

[granddad]

Hi Nikolai , had you looked at 723 Reg IC .

The 723 Voltage Regulator IC. It consists of a voltage reference source (Pin 6), an error amplifier with its inverting input on pin 4 and non-inverting input on pin 5, a series pass transistor (pins 10 and 11), and a current limiting transistor on pins 2 and 3. The device can be set to work as both positive and negative voltage regulators with an output voltage ranging from 2 V to 37 V, and output current levels up to 150 m A. The maximum supply voltage is 40 V, and the line and load regulations are each specified as 0.01%.

Edit , Changed the original jpg circuit as it had pins 11 and 10 connected ?

 

[Nigel Goodwin]

He said he can't get those, for what ever reason?

Just because he said something doesn't mean it makes any sense

 

[audioguru]

He said he can't get those, for what ever reason?

He is in Vietnam (or on the Moon?) where common ordinary Western parts are not available.

 

[Mikebits]

They don't do Ebay there?

 

[large_ghostman]

They got the internet so unless its on a import ban............ Besides didnt he order from RS? I am reasonably sure RS do a couple of different regulators

 

[Nikolai Petrenko]

Oh my question spend all you a lot of time. Thank for all answers.
I can't find 723 reg IC.
78xx series are vulnerable to input voltage above 35V. LM317 is better anyway, will safe when input voltage below 40V. But only TO-3 and 220 version of LM317 are available, TO-92 not.
Yes, as AG said, in my country many common Western are not available. But seem be Japanese and European parts are much popular than American ones. Japanese parts are pretty variety. Russian parts quite popular, but most are old power analog parts like diodes, transistors, thyristors in since Soviet-era (good for high power).
Lucky! Return to my old thread "Transistors equivalent", I have found that KT135G will replace BF494 or BF109 well in RF circuits, some name-faded glass diode will replace 1N34 quite well (may by germanium diode), all of these were extract from old Soviet radio walkie-talkie .

 

[Nikolai Petrenko]

I realized that parts in chipdip.ru are cheaper and more reliable than in Ebay ( part of Ebay which I can reach, not all).

 

[large_ghostman]

I realized that parts in chipdip.ru are cheaper and more reliable than in Ebay ( part of Ebay which I can reach, not all).

Mate you so need to move!! Life without a fully stocked parts bin is just existing and not living, build a raft